Along with increase of communications traffic these days, construction of a large capacity system is required for an optical transmission system. As an optical transmission system that can cope with such capacity increase, there are various multiplex systems of such as wavelength multiplexing, time division multiplexing and optical polarization division multiplexing, for example. Then, an optical receiving apparatus that is used for such optical transmission systems is disclosed in patent literature 1, for example.
A receiver of patent literature 1 can take out a desired channel stably from a received signal by extracting a carrier and one optical signal in the short wavelength side or in the long wavelength side from the received optical signal, and suppressing phase components in the short wavelength side and the long wavelength side from counteracting each other at the time of photoelectric conversion.
Here, in addition to that, various technologies to improve the reception characteristics by performing some correction to a received optical signal have been also proposed.
For example, in patent literature 2, there is disclosed a technology to improve optical transmission quality by adjusting the property of an edge band part and the property in the center region part in a super channel signal based on system information such as the network topology of an optical transmission system.
Also, in patent literature 3, there is disclosed a technology to improve transfer characteristics deterioration due to an error between an optical signal wavelength and the transmission center wavelength of an optical multiplexer/demultiplexer using an optical filter for spectral shaping, thereby improving tolerance to a wavelength error.
Furthermore, there is disclosed in patent literature 4 a technology to reduce influence of waveform deterioration by performing phase-modulation in such a way that opposite optical frequency shifts are caused in the first half and the second half of an optical pulse.